Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 1 - By Alexander Von Humboldt And Aime Bonpland.
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The Variable Pressure On The Surface Of The Sea, Caused By The
Changes In The Weight Of The Air, Is Another Cause Of Motion Which
Deserves Particular Attention.
It is well known, that the
barometric variations do not in general take place at the same
moment in two distant points, which are on the same level.
If in
one of these points the barometer stands a few lines lower than in
the other, the water will rise where it finds the least pressure of
air, and this local intumescence will continue, till, from the
effect of the wind, the equilibrium of the air is restored. M.
Vaucher thinks that the tides in the lake of Geneva, known by the
name of the seiches, arise from the same cause. We know not whether
it be the same, when the movement of progression, which must not be
confounded with the oscillation of the waves, is the effect of an
external impulse. M. de Fleurieu, in his narrative of the voyage of
the Isis, cites several facts, which render it probable that the
sea is not so still at the bottom as naturalists generally suppose.
Without entering here into a discussion of this question, we shall
only observe that, if the external impulse is constant in its
action, like that of the trade-winds, the friction of the particles
of water on each other must necessarily propagate the motion of the
surface of the ocean even to the lower strata; and in fact this
propagation in the Gulf-stream has long been admitted by
navigators, who think they discover the effects in the great depth
of the sea wherever it is traversed by the current of Florida, even
amidst the sand-banks which surround the northern coasts of the
United States.
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